Oxford and Cambridge Tips, Please

To Cambridge buy a Super off Peak Day Return for £20.70 from Kings Cross on Great Northern. No matter how early you travel this is a walk up fare, valid on any return train

To Oxford buy single advance fares on Great Western from Paddington for £12 each way (the cheaper £6 fares are sold out)- cheaper than a £31.80 walk up Off Peak Day Return

If you have a railcard, then normal discounts apply.

Before you head to Cambridge , check to see if visitors are allowed that day . Sunday appears to be Easter and the spring term begins 4/25 This may be examination time and colleges may be closed to visitors during that period

That's Easter weekend so the trains may be crowded. The 10th is Easter Monday which is a bank holiday in the UK. You might think of buying train tickets ahead of time. They won't run out of tickets but they may run out of seats. That means you stand the entire way.

For just one day in Oxford, you might try https://visit.bodleian.ox.ac.uk/tours which I believe opens for tickets only one month before the date you want. My husband and I greatly enjoyed the 90-minute tour.

Also pleasant is the City of Oxford Walking Tour: https://tickets.ox.ac.uk/WebStore/shop/ViewItems.aspx?CG=bodgroups&C=BODCWT You can book @ two months in advance.
Ashmolean Museum: https://www.ashmolean.org/plan-your-visit#widget-id-2152791. You can book @ 2 months in advance. Free admission OR you can make a donation.

If I had just one day, I would probably not go to a museum. Oxford is best experienced (in my opinion) from the outside walking around the colleges--Christ Church and Magdalen College are especially lovely. Walking to South Park and viewing the spires of Oxford from the top was one of my favorite moments.
No1 Ship Street Oxford is a great restaurant.
The same is true of Cambridge--walk around the city and view the architecture.

King’s College Chapel and college gardens: https://www.kings.cam.ac.uk/visit/your-visit. Book @2months in advance.

Oxford and Cambridge are two of my favorite places to visit.

Note that on Easter Monday to Cambridge, although you can buy advance tickets, all three companies on their different lines, do NOT provide seat reservations, as these are commuter railroads.
All an advance ticket does is provide a cheaper fare (which doesn't work on return fares, only singles)- 2 advance tickets are more than an open day return, it does NOT guarantee a seat.
The same applies to Oxford services- on both the Marylebone route (whose fares are dearer than Great Western that day) or the Paddington route, suggested above.
The same is true on most of Northern Rail, and on most other short distance commuter railroads in SE England.

with trips on Good Friday and Easter Monday you will need to check VERY carefully for closures and reduced hours. Churches and chapels may well be out completely on Good Friday. Check carefully.

The Fitz will be open in Cambridge on Friday but not on Monday (never open on Monday) and has good exhibits and collections.

Fitzbillies, renowned for their sticky chelsea buns - people come from miles around for a bun at Fitzbillies, is across the street from the Fitz. (Fitzwilliam Museum on Trumpington Street).

Cambridge University Botanic Garden is open every day (excellent home made sausage rolls (meat or vegan) at the cafe are excellent) and snowdrops are finishing but crocuses and other spring bulbs are popping.

Schools will be on holiday across England so expect trains and museums to be very busy.

I'd look for a walking tour offered by either the university or the city tourist office. (I don't remember which I used in each city.) They--especially university-run tours--are more likely than commercial tours to have access to colleges during difficult periods like exam time.

In Cambridge: the Eagle Pub. WW II connectons and the place where Watson and Crick first announced their discovery of the structure of DNA.